This invention relates to a method for preparing carboxylic acid esters from halocarbons, more particularly to the preparation of carboxylic acid esters by reacting a halocarbon with a salt in an organic liquid.
Carboxylic acid esters (including mono-, di, and higher esters) such as propylene glycol diacetate, allyl acetate and glycerine triacetate are useful as solvents, lacquers, plasticizers and the like in a variety of commercial applications. For example, glycerine triacetate is used in the treatment of acetate fibers for cigarette filters. Other esters are useful as retarder solvents in high baked automotive coatings, as coalescing agents in aqueous and solvent based paints, as effective cleaning agents in polyester resin cleaning equipment and to harden core sands used in foundry industry.
There are a variety of commercially employed methods for synthesizing organic esters, diesters and triesters. For example, in the preparation of carboxylic acid esters, it is known that alcohols will react with a carboxylic acid anhydride, a carboxylic acid or their combination, in the presence of an acid catalyst such as sulfuric or hydrochloric acid, to form a carboxylic acid ester. Unfortunately, the acid catalyst water as well as a variety of by-products in the resulting reaction product often make recovery of the desired reaction product difficult.
Several alternative methods have been proposed for preparing an organic diester. One such method is described in U.S. Pat. No. 2,115,905. In the described method, a glycol diester is prepared by reacting an alkylene dichloride and an alkali or alkaline earth metal salt of a fatty acid in the presence of a small amount of water. Unfortunately, the described reaction comprises a two phase reaction mixture, i.e., one phase comprising the carboxylic acid salt and the other phase comprising the alkylene dichloride, which results in mixing and handling difficulties as well as reduced organic ester selectivity. In addition, further increases in the yield of the glycol diesters are desired.
Alternatively, U.S. Pat. No. 3,461,156 describes a method for producing carboxylic acid esters by reacting the corresponding acid with a halocarbon in the presence of an alkali metal hydroxide and a mutual solvent consisting of dimethylformamide (DMF), dimethyl sulfoxide (DMSO) or mixtures of the two. The solvent may also comprise water The amounts of water in the DMF and DMSO affect the yield of the carboxylic acid ester, with a solvent having from 10 to 25 percent by volume water being preferred. Unfortunately, the stated yields and product purification processes are commercially undesirable.
Yet another method for preparing a glycol ester is described in U.S. Pat. No. 4,298,758. The method comprises reacting a dichloroisopropyl ether with a carboxylic acid and an alkali metal salt thereof. Unfortunately, due to cleavage of the ether, the reaction product is a mixed reaction product comprising a major portion of dipropylene glycol diacetate and a smaller portion of propylene glycol diacetate. In addition, the monoacetate of propylene glycol and 1-chloro-1-acetoxy-bis(2,2-oxy-propane) are present in the reaction product.
In German Patent 41,507, it is taught that benzyl chloride or ethylene dichloride can be reacted with sodium acetate in acetic acid. In the example of this German patent, the reaction of ethylene dibromide with sodium acetate is described in more detail. With benzyl chloride, however, high reactivity naturally produces high yields that are not obtainable with aliphatic halocarbons. Ethylene dichloride does not tend to produce undesired by-products like halocarbons with more carbon atoms. Furthermore, there is no mention of the criticality to remove water from the reaction mixture since it is not important with these two halocarbons.
Propylene glycol diacetate is produced according to a known, commercially used, process by reacting propylene oxide and water to give propylene glycol which is then converted with acetic acid to propylene glycol diacetate. Glycerol triacetate is commercially produced by reacting glycerol and acetic acid. The commercial processes are disadvantageous since valuable propylene oxide and glycerol are required as starting materials.
In view of the stated deficiencies of the prior art methods for preparing carboxylic acid esters from halocarbons, it remains highly desirable to provide a method for effectively preparing an organic ester at relatively high yields from inexpensive starting materials.